This invention relates to a process for preparing pigment compositions having improved rheology and brightness by surface treating organic pigments with combinations of certain sterically hindered and/or bulky primary amines and certain pigment derivatives.
Surface treatment is a type of finishing in which certain auxiliaries, such as rosin or other resins, are applied to pigments to influence their surface structure and thus their physical and coloristic properties. E.g., W. Herbst and K. Hunger, Industrial Organic Pigments (New York: VCH Publishers, Inc., 1993), pages 205-207. Surface treatment is a particularly useful method for improving pigment dispersibility in inks, toners, paints, coatings, and plastics.
The use of amines or amine derivatives in the preparation of pigment dispersions is known. For example, Czech Patent 227,779 discloses a two-step process for dispersing organic pigments in inks by first dispersing the pigments in the presence of ampholytic sulfonates of C.sub.12 -C.sub.24 fatty acids and then coagulating the dispersed pigments with hydrophobic alkyl amines or ethoxylated C.sub.12 -C.sub.24 fatty acids. European Patent Application 544,441 discloses dispersions of organic pigments in which the pigment is treated with a non-polar additive and dispersed in a solution containing a polar additive, including certain rosin amines or multifunctional amines. However, these two patents, besides requiring two-step treatments using two different types of dispersants, do not disclose the use of the sterically hindered and/or bulky primary amines that are a critical feature of the present invention.
Japanese Patent 63/305,172 discloses the dispersion of organic pigments in inks in the presence of certain surfactants, including stearylamine and stearylpropyleneamine. This patent, however, does not disclose the treatment of organic pigments with sterically hindered and/or bulky primary amines.
U.S. Pat. No. 4,929,279 discloses aqueous dispersions prepared by adding certain surfactants to an aqueous slurry of the pigment and then subjecting the treated pigment to ultrasonic irradiation. The surfactants include narrowly defined groups of diamines having two tertiary amino groups, two quaternary ammonium groups, or a combination of a secondary amino group with a primary amino group. This patent, however, does not disclose the treatment of organic pigments with the sterically hindered and/or bulky primary amines that are a critical feature of the present invention.
Certain ring-substituted pigment derivatives, such as sulfonamides, carboxamides, and heterocyclic-containing groups, have been reported to improve pigmentary properties. E.g., U.S. Pat. Nos. 5,457,203, 5,453,151, 5,424,429, 5,368,641, 5,334,727, 5,286,863, 5,264,032, 5,229,515, 5,194,088, 5,145,524, 5,137,576, 4,895,949, 4,844,742, 4,541,872, 4,478,968, 4,455,173, 4,439,240, 4,256,507, and 4,310,359. Such pigment derivatives, however, have not been used in conjunction with sterically hindered and/or bulky primary amines such as required in the present invention.
Surface treatment of organic pigments with mixtures of certain sterically hindered and/or bulky primary amines is known. For example copending U.S. application Ser. No. 08/769,477 (filed Dec. 20, 1996) now U.S. Pat. No. 5,728,206 discloses the use of a narrowly defined group of tertiary alkyl primary amines. Copending U.S. application Ser. No. 08/769,478 (filed Dec. 20, 1996) now U.S. Pat. No. 5,741,356 discloses the use of a broader class of sterically hindered and/or bulky primary amines but additionally requires ultrasonic irradiation during surface treatment. The process of the present invention, however, provides improved rheology and pigmentary properties without the need for ultrasonic irradiation.
The treatment of organic pigments with mixtures of sterically hindered and/or bulky primary amines and pigment derivatives according to the present invention provides pigment compositions having improved rheology and brightness that are particularly suited for use in high-solids coating compositions.